Wells are often drilled for the production of petroleum fluids from subterranean reservoirs. In many cases, a drill bit is connected to a drill string and rotated by a surface-based drilling rig. Drilling mud is circulated through the drill string to cool the bit as it cuts through the subterranean rock formations and to carry cuttings out of the wellbore. The use of rotary drill bits and drilling mud is well known in the art.
As drilling technologies have improved, “measurement while drilling” techniques have been enabled that allow the driller to accurately identify the location of the drill string and bit and the conditions in the wellbore. MWD equipment often includes one or more sensors that detect an environmental condition or position and relay that information back to the driller at the surface. This information can be relayed to the surface using acoustic signals that carry encoded data about the measured condition.
Prior art systems for emitting these acoustic signals make use of wave generators that create rapid changes in the pressure of the drilling mud. The rapid changes in pressure create pulses that are carried through the drilling mud to receivers located at or near the surface. Prior art pressure pulse generators, or “mud sirens,” include a single stator, a single rotor and a motor for controllably spinning the rotor. The selective rotation of the rotor temporarily restricts and releases the flow of mud through the mud siren. By controlling the rotation of the rotor, the mud siren can create a pattern of pressure pulses that can be interpreted and decoded at the surface.
Although generally effective, prior art mud sirens may experience bandwidth limitations and signal degradation over long distances due to weakness of the pressure pulses. Accordingly, there is a need for an improved mud siren that produces a stronger pressure pulse that will travel farther and carry additional data. It is to this and other deficiencies in the prior art that the present invention is directed.